1. Field of the Invention
The present invention relates to a method of drawing a pattern by direct writing with a charged particle beam using a resist, in electron beam direct writing.
2. Description of the Related Art
In a manufacturing method of a semiconductor apparatus, the density of the apparatus is generally becoming higher and higher. Especially, in a lithography for exposing a fine pattern on a semiconductor wafer, the design rule is becoming finer. An X-ray lithography using an X-ray, or a charged particle beam lithography using a charged particle beam, instead of an optical lithography using a ultraviolet light, is being developed as the next generation lithography.
In the charged particle beam lithography, a substrate pattern 30 is formed by patterning a substrate layer formed on a substrate 20 as illustrated in FIG. 6. Here, the pre-process of patterning a substrate layer is completed.
As illustrated in FIG. 7, a resist film 50 is formed by applying a resist on the substrate 20 having the substrate pattern 30 formed. An electron beam (charged particle beam) 40 is applied to this resist film 50 and a writing pattern is formed by its development.
The resist film 50 consists of a base resin, photooxidation agent, cross linking agent, dissolution inhibitor, and the like, and oxide is generated by irradiation of the electron beam (charged particle beam) 40. The generated oxide causes the elimination reaction of protecting group of the base resin, or the ligand bridged reaction of the resin, thereby changing the solubility characteristic for the developer. This produces difference in the solubility for the developer between an irradiated portion and a non-irradiated portion, thereby enabling patterning.
As illustrated in FIG. 8, in a charged particle beam exposure, exposure amount is adjusted depending on the density of a writing pattern, in order to correct the proximity effect in the substrate pattern 30 of a layer to be written. Alternatively, auxiliary exposure by a defocus beam makes constant, the accumulation energy within the resist film 50 concerned with the pattern writing. In these ways, the proximity effect depending on the pattern of a layer to be written can be corrected.
The reference numeral 90 indicated by the broken line in FIG. 8 is a design data pattern, and the reference numeral 100 indicated by the solid line is an actual exposure pattern.
The conventional pattern drawing method is able to correct the proximity effect concerned with the writing pattern. However, since the device is formed by overlapping a plurality of layers including an element separation layer, a conductivity contact layer, a wiring layer, and the like, it is subjected to the effect of the pattern on the substrate pattern 30 which has been formed in the pre-process, in addition to the proximity effect generated in a layer to be written. This is because the scattering degree of electron beam depends on the existence of the substrate pattern 30, thereby to change the writing density, in the electron beam exposure.
Therefore, the conventional method has such a problem that the effect of the substrate pattern 30 deteriorates the drawing accuracy of a writing pattern. For example, when there exists a wiring pattern of a heavy metal as the substrate of a writing pattern, backscattering of an electron beam in an area having the substrate of the heavy metal (reflected electron 60 rebounded from the area having the substrate pattern 30 as illustrated in FIG. 7) is greater than that of a reflected electron 70 in an area having no substrate. This means that writing in the area having the substrate pattern is actually performed at higher exposure amount. Therefore, it has such a problem that the actual pattern of an actual exposure pattern 100 in the area having the substrate becomes greater than the design data pattern 90 obtained in the stage of design.